The present invention is directed to a method and apparatus for converting a top tube sheet precoat filter apparatus to a bottom tube sheet precoat filter apparatus.
Precoat filter apparatus of the top tube sheet design are well known in the art. The typical top tube sheet precoat filter apparatus includes a filter tank which is divided into an upper effluent compartment and a lower influent compartment by a generally horizontal tube sheet secured in place at the intersection between the upper and lower sections thereof. A plurality of downwardly extending precoat filter elements are suspended from the tube sheet within the influent compartment in fluid communication with openings formed in the tube sheet. An influent conduit directs liquid to be treated into the lower influent compartment and an effluent conduit directs treated liquid from the upper effluent compartment. The filter elements used in this design are of the stainless steel mesh or wire wound type which have provided notably poor performance in critical treatment applications, such as main condensate polishing at nuclear power stations. Such poor performance is as a consequence of precoat material leakage, poor precoat material utilization due to ineffective distribution of the precoat material onto the filter elements, and ineffective removal of spent precoat material from the filter elements due to utilization of a sub-standard backwash technique known as "air bump" , which is necessarily employed with this filter apparatus design.
Precoat filter apparatus of the bottom tube sheet design are also well known in the art, an example of which is disclosed in U.S. Pat. No. 3,715,033, assigned to the same assignee as the present invention. The typical bottom tube sheet precoat filter apparatus includes a filter tank which is divided into an upper influent compartment and a lower effluent compartment by a generally concave tube sheet secured in place in a lower portion of the filter tank. A plurality of precoat filter elements extend upwardly from the tube sheet within the upper influent compartment in fluid communication with openings formed in the tube sheet. An influent conduit extends upwardly through openings in the bottom of the filter tank and the tube sheet for directing liquid to be treated into the upper influent compartment and an effluent conduit directs treated liquid from the lower effluent compartment. The filter elements utilized in this design are of the fiber-wound type. These filter elements substantially eliminate precoat material leakage and achieve improved precoat material utilization due to superior distribution of the precoat material on the filter elements. Further, this design typically utilizes the backwash technique known as "air surge" which maintains a superior condition of the filter elements.